The present invention is related to a disposable safety syringe. The inner circumference of front end of the barrel of the syringe is formed with a conic section. When the piston stem is forcedly pushed inward to drive the needle holder, the click hooks thereof is pressed against the conic section and converged and located. Accordingly, the piston stem can drive the needle holder to move rearward and make the click hooks pass through the flange of inner circumference of the barrel so as to retract the needle holder into the barrel.
FIG. 9 shows a conventional safety syringe. The inner circumference of front section of the barrel 81 is formed with a flange 811. The needle holder 82 fitted in the barrel 81 is formed with a recessed section 821 corresponding to the flange 811. By means of engagement between the flange 811 and the recessed section 821, the needle holder 82 can be located in the barrel 81. The needle holder 82 has an insertion tube 822 for fitting with an injection needle 83. The inner circumference of the needle holder 82 is formed with two click hooks 823. The front end of the piston 841 of the piston stem 84 is formed with an engaging section 842 corresponding to the click hooks 823.
In use, the injection needle 83 is first fitted with the insertion tube 822 of the needle holder 82. Then, the piston stem 84 is pushed forward to a predetermined position and then pulled rearward so as to suck the medicine into the barrel 81. After injection, the piston stem 84 is pushed forward to make the engaging section 842 fit into the needle holder 82. At this time, the click hooks 823 are engaged with the engaging section 842 to prevent the piston stem 84 from departing from the needle holder 82 as shown in FIG. 10. Accordingly, when pulled rearward, the piston stem 84 can drive the needle holder 82 to move and make the recessed section 821 disengage from the flange 811. Under such circumstance, the needle holder 82 can be retracted into the barrel 81 along with the piston stem 84. Accordingly, the injection needle 83 is prevented from protruding outward so as to avoid impalement of medical personnel.
The needle holder 82 is fixed only by means of the engagement between the flange 811 and the recessed section 821. In the case that the flange 811 more protrudes from the inner circumference of the barrel 81, the flange 811 will be able to more tightly engage with the recessed section 821 to achieve greater fixing force and prevent the needle holder 82 from moving rearward when inserting the injection needle 83. However, after the engaging section 842 of the piston stem 84 is engaged into the needle holder 82, the needle holder 82 will be hard to be driven and retracted into the barrel 81. In the case that the flange 811 less protrudes from the inner circumference of the barrel 81, the flange 811 is not so tightly engage with the recessed section 821 and the fixing force is less. Accordingly, after the engaging section 842 of the piston stem 84 is engaged into the needle holder 82, the needle holder 82 can be easily driven and retracted into the barrel 81. However, when inserting the injection needle 83, the needle holder 82 can be hardly truly fixed in the barrel 81 and is likely to be pushed rearward.
Furthermore, when the piston stem 84 is first pushed forward prior to filling of the medicine or bleeding and then pulled rearward to suck the medicine or blood, it often takes place that the engaging section 842 of the piston stem 84 are engaged with the click hooks 823 of the needle holder 82 without departure. Under such circumstance, the syringe must be discarded to use a new syringe. This leads to waste of resource.
It is therefore a primary object of the present invention to provide a disposable safety syringe. The inner circumference of front end of the barrel of the syringe is formed with a conic section. When the piston stem is forcedly pushed inward to drive the needle holder, the click hooks thereof is pressed against the conic section and converged and located. Accordingly, the piston stem can drive the needle holder to move rearward and make the click hooks pass through the flange of inner circumference of the barrel so as to retract the needle holder into the barrel and ensure safety.
The present invention can be best understood through the following description and accompanying drawings wherein: